1. Technical Field
The present invention relates to a gyro sensor and an electronic device including this gyro sensor, and more particularly to a gyro sensor capable of preventing damage to and adhesion of a drive system of the gyro sensor and to an electronic device including this gyro sensor.
2. Related Art
As known in the art, a gyro sensor is equipped on electronic devices such as digital cameras, video cameras, cellular phones, and automotive navigation systems to detect an angular velocity of the devices for position control or the like. An MEMS (micro electro mechanical system) capacitance gyro sensor includes a driving system and a detecting system, and determines an angular velocity based on a Coriolis force generated in the detecting system when an angular velocity is applied to the driving system oscillating at a constant oscillation frequency and to the detecting system interlocked with the driving system, regarding this force as a change of the capacitances of the detecting system (movable electrode) and a fixed electrode. According to this structure, the driving system is often disposed in such a position as to surround the outside of the detecting system. Also, there are often provided two units arranged side by side each including the driving system and the detecting system so as to cancel the acceleration components and detect only the angular velocity. In this case, the two driving systems are driven in the opposite phases and oscillate in the opposite directions. Therefore, when a physical amount such as an excessive voltage is applied to the driving electrode of the gyro sensor or when the gyro sensor drops, collision between the driving system and the element disposed outside or between the two driving systems may occur, producing risk of damage to the gyro sensor. Moreover, particularly in the case of a gyro sensor including silicon, charges generated on the surfaces of the electrodes are attracted to each other, in which condition the electrodes adhere to each other and are difficult to be separated therefrom in some cases.
There is disclosed in JP-A-2002-228680, a capacitance mechanical sensor provided with a movable electrode which shifts in accordance with a physical amount, and a fixed electrode which faces to the movable electrode with a small clearance left therebetween. According to this sensor, a projection is formed on at least one of the movable electrode and the fixed electrode to produce a height difference from the one electrode provided with the projection to the other electrode, so that adherence between the movable electrode and the fixed electrode can decrease. This projection is provided for the purpose of preventing adhesion between the electrodes or between a fixed portion and a weight portion.
According to the capacitance mechanical sensor disclosed in JP-A-2002-228680, however, it is required to increase the distance between the electrodes by the length corresponding to the projection disposed on the side of the fixed electrode opposed to the movable electrode. In this case, size reduction of the elements becomes difficult.